Somewhere in the forum is the formula that a number of participants have concluded. I claim no original thought in this, but here is roughly how it works:

Point values are based only on the length of the puzzle. Difficult (short) quotes start out being worth 450 points, Average 300 points and Easy (long) quotes 150 points. The logic appears to be that the fewer letters you have to work with, the more difficult it is to solve. There has been much discussion about this not making much sense, but we don't make the rules.

For each 6 seconds that is required to solve, the score is reduced by one point.

If I did not render this accurately, someone can chime in and correct it.